基于多轴强度准则的混凝土面板应力安全评价方法研究

Evaluation method for safety of concrete slab stress based on multi-axial strength criterion

混凝土面板作为面板堆石坝的关键防渗结构,其应力变形安全对保障工程安全运行至关重要。目前工程中普遍采用混凝土单轴标准强度评价面板应力安全,该方法忽略了面板应力状态对其强度的影响,会对面板破坏范围作出不合理的判断,因此,提出了基于多轴强度准则的混凝土面板应力安全评价方法,该方法通过确定混凝土强度调整系数及多轴强度应力水平指标评价面板应力安全。联合基于位移多点约束法的面板精细化计算方法及改进黏弹性方法全面考虑动位移和永久变形对面板动应力的影响,细致模拟地震过程中面板破坏发展过程。以强震区狭窄河谷上240 m级特高面板坝为例,对比分析了文中提出的多轴强度方法与当前单轴强度方法判断面板破坏范围的差异,结果表明:正常蓄水期,坝肩两侧面板位于“抗压强度削减区”、河床面板均位于“抗压强度增强区”,其中河床底部面板强度增加尤为明显,两种方法判断的面板受拉破坏区基本一致,但受压破坏区存在较大差异;遭遇地震情况下,多轴强度方法判断的面板受拉破坏区略小,而两种方法受压破坏区的位置和大小均存在显著差异。鉴于单轴强度方法无法考虑面板应力分布对其强度的影响,建议采用多轴强度准则指导特高面板坝混凝土面板设计和施工。

The concrete-faced rockfill dams(CFRDs)rely on the key impermeable structures,such as concrete slabs,for their safe operation.Ensuring the safety of the concrete slabs is of the utmost importance.The current evaluation method,which utilizes uniaxial strength,overlooks the influences of slab stress on their strength and may lead to unreasonable judgments regarding the damage zone.To address this issue,a method is proposed for evaluating the stress in the concrete slabs based on the multi-axial strength criterion.The safety of the slabs is assessed by determining the strength adjustment coefficient of concrete and the stress level index of multi-axial strength.A refined stress distribution analysis of the slabs is conducted using the cross-scale fine simulation method based on the multi-point constraint.The improved viscoelastic method is employed to comprehensively simulate the impact of dynamic and permanent deformations on the slab stress.This approach accurately depicts the progression of slab damage during an earthquake.To illustrate the effectiveness of the proposed multi-axial strength method,a 240 m-high concrete-faced rockfill dam located in a narrow valley within a seismic zone is taken as an example for comparison with the current uniaxial strength method.The results demonstrate that during the operational period,the material strength at both sides of the dam abutment is reduced,while it is enhanced on the riverbed,particularly at the bottom.Both methods yield similar conclusions regarding the tensile damage zones,but there are significant disparities in the compressive damage zones.During an earthquake,the multi-axial strength method indicates slightly smaller tensile damage zones,whereas the location and extent of the compressive damage zones differ significantly between the two methods.Considering the limitations of the uniaxial strength method in considering the influences of slab stress on their strength,it is suggested to adopt the multi-axial strength criterion as a guide for designing and constructing concrete slabs in extra-high CFRDs.